Physical data storage media, such as removable storage media, have a fixed capacity for data. For example, Digital Versatile Disk (DVD) is an optical media that encodes information on a circular plastic disk and can contain approximately 4.7 GB of data in a single sided, single layer format. A Compact Disk (CD) is a similar medium that can store approximately 700 MB of data.
In many cases, media such as DVD and CD may use forward error correcting techniques to encode additional redundant data within the data stream. When a portion of the data is unreadable or is deemed corrupt from a checksum, for example, the corrupted or unreadable data may be recreated using the redundant data. In many cases, the redundant data is interlaced or otherwise incorporated into the main data.
Data storage media are susceptible to corruption or data loss through various mechanisms. As data storage media increase in capacity, the likelihood of failures of individual bits increases given the billions and trillions of individual bits that may be stored. Such failures may be corrected using forward error correction techniques. However, other data loss mechanisms may damage the data along with forward error correction data that may be used for recovery. An example of such a data loss mechanism may be a scratch or other local damage to an optical medium.